Lubricating systems for regenerative vacuum pumps

ABSTRACT

In a vacuum pump of the regenerative type or including a regenerative section in which a rotatable substantially vertical shaft is supported by upper and lower bearings, a lubricating system for lubricating the bearings comprising an axial bore extending along the shaft and in communication with radial holes aligned respectively with the lower bearing and the upper bearing, the lower open end of the axial bore extending in to a shaft reservoir containing lubricating fluid, and in which the radial holes in alignment with the lower bearing are formed in a tapered surface of the axial bore

FIELD OF THE INVENTION

[0001] This invention relates to vacuum pumps of the regenerative typeor which incorporate a regenerative section and which incorporate a highspeed rotatable vertical shaft supported by bearings at each end of theshaft, and in particular to lubricating systems for such bearings.

BACKGROUND OF THE INVENTION

[0002] In vacuum pumps of the regenerative type, a rotor is mounted on avertical shaft for rotation within a surrounding stator. The shaft issupported by upper and lower bearings which require lubrication. Tofacilitate lubrication of the bearings the shaft is provided with acentral axial bore which communicates with radial holes in alignmentwith the upper and lower bearings for delivering a lubricating fluid tothe bearings.

[0003] It is known to utilise centrifugal force generated by therotating shaft to draw the lubricating fluid from a reservoir up theaxial bore in the form of a thin film to reach the radial holes inalignment with initially the lower bearing and finally the upperbearing. The lubricating fluid establishes its own taper in a straightaxial bore provided that a small ledge is available at the lower end ofthe axial bore. In known lubricating systems the radial holes inalignment with the lower bearing terminate the taper and thus preventfurther flow up the axial bore thereby starving the upper bearing oflubrication.

[0004] It is an aim of this invention to obviate this disadvantage.

SUMMARY OF THE INVENTION

[0005] According to the present invention, in a vacuum pump of theregenerative type or including a regenerative section in which arotatable vertical shaft is supported by upper and lower bearings, alubricating system for lubricating the bearings comprises an axial boreextending along the shaft and in communication with radial holes alignedrespectively with the lower bearing and the upper bearing, the loweropen end of the axial bore extending in to a shaft reservoir containinglubricating fluid, and in which the radial holes in alignment with thelower bearing are formed in a tapered surface of the axial bore.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] An embodiment of the invention will now be described, by way ofexample, reference being made to the Figures of the accompanyingdiagrammatic drawings in which:

[0007]FIG. 1 is a cross section through a known compound vacuum pumpincluding a regenerative section;

[0008]FIG. 2 is a detail of a known lubricating system illustrating howlubricating fluid establishes its own taper in a straight axial bore;

[0009]FIG. 3 is a detail similar to FIG. 2 but illustrating how in theknown art excessive lubricating fluid can be delivered to the lowerbearing whilst insufficient lubricating fluid is delivered to the upperbearing; and

[0010]FIG. 4 is a detail similar to FIGS. 2 and 3 but illustrating thelubricating system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Referring first to FIG. 1, which illustrates a known compoundvacuum pump comprising a regenerative section 1 and a molecular drag(Holweck) section 2. The pump includes a casing 3 made from a number ofdifferent body parts bolted or otherwise fixed together and providedwith relevant seals therebetween.

[0012] Mounted within the casing 3 is a vertical shaft 6 supported by anupper bearing 4 and a lower bearing 5. The shaft 6 is rotatable aboutits longitudinal axis and is driven by an electric motor 7 surroundingthe shaft 6. Securely attached to the shaft for rotation therewith is arotor 9. An axial bore 8 extends along a substantial length of the shaftand communicates with radial oil holes 8′ delivering lubricating fluidto the upper and lower bearings.

[0013] Referring now to FIG. 2, it is known that a lubricating fluidsuch as oil establishes its own taper in a straight axial bore providinga small ledge is available at the bottom (as shown) end of the axialbore.

[0014] Referring now to FIG. 3, it is known to provide two sets ofradial holes 14, 12 which communicate at one end with the axial bore 18of a rotatable shaft 16 and respective upper and lower bearings (notshown). When the shaft 16 rotates, centrifugal force will forcelubricating fluid from a reservoir through an open lower end of theshaft 16 and along the inside surface of the axial bore in the form of athin film. However, the lower radial holes 12 effectively finalise thetaper of the lubricating fluid film and prevent further flow of the filmup the axial bore thereby starving the upper bearing of lubrication.

[0015] According to the present invention and with reference to FIG. 4the lower radial holes 12 in alignment with the lower bearing are formedin a tapered surface of the axial bore. This mechanical taper means thatthe lubricating fluid will continue to flow both out from the lowerradial holes 12 and also past the holes 12 to the upper radial holes 14to the upper bearings.

[0016] The ratio of lubricating fluid leaving the respective holes 12,14 is dependent upon oil jet hole diameter, taper angle, hole heightwithin the taper and taper diameter.

1. In a vacuum pump of the regenerative type or including a regenerativesection in which a rotatable substantially vertical shaft is supportedby upper and lower bearings, a lubricating system for lubricating thebearings comprising an axial bore extending along the shaft and incommunication with radial holes aligned respectively with the lowerbearing and the upper bearing, the lower open end of the axial boreextending in to a shaft reservoir containing lubricating fluid, and inwhich the radial holes in alignment with the lower bearing are formed ina tapered surface of the axial bore.
 2. In a vacuum pump of theregenerative type or including a regenerative section in which arotatable substantially vertical shaft is supported by upper and lowerbearings, a lubricating system for lubricating the bearings comprisingan axial bore extending along the shaft and in communication with radialholes aligned respectively with the lower bearing and the upper bearing,the lower open end of the axial bore extending in to a shaft reservoircontaining lubricating fluid, and in which the radial holes in alignmentwith the lower bearing are formed in a tapered surface of the axial boreand lower bearings, a lubricating system constructed and arrangedsubstantially as hereinbefore described with reference to FIG. 4 of theaccompanying drawings.